Hydrophilic DLC on substrate with UV exposure

ABSTRACT

A substrate is coated with a layer(s) or coating(s) that includes, for example, amorphous carbon in a form of diamond-like carbon (DLC). In certain embodiments, the DLC inclusive layer may be doped with at least one polar inducing dopant (e.g., Boron, Nitrogen, and/or any other suitable polar inducing dopant) in order to make the layer more polar and thus more hydrophilic so as to have a lower contact angle θ. In other embodiments, where such doping is optional, the DLC may be exposed to ultraviolet (UV) radiation in a manner sufficient to cause the contact angle θ of the DLC layer to drop into a hydrophilic range (e.g., less than or equal to about 20 degrees).

This application is a continuation of application Ser. No. 10/675,975,filed Oct. 2, 2003, now U.S. Pat. No. 6,793,979, which is a divisionalof application Ser. No. 09/987,692, filed Nov. 15, 2001, now U.S. Pat.No. 6,713,179, which is a continuation-in-part (CIP) of U.S. patentapplication Ser. No. 09/899,176, filed Jul. 6, 2001 (now U.S. Pat. No.6,592,992), which is a division of U.S. patent application Ser. No.09/577,337, filed May 24, 2000 (now U.S. Pat. No. 6,303,225), thedisclosures of which are hereby incorporated herein by reference.

This invention relates to a hydrophilic coating including diamond-likecarbon (DLC) provided on (directly or indirectly) a substrate of glass,plastic, or the like, and a method of making the same. Moreparticularly, this invention relates to a DLC inclusive coating that isexposed to at least ultraviolet (UV) radiation in order to cause thecoating to either become hydrophilic or become more hydrophilic (i.e.,to cause contact angle θ of the coating to decrease).

BACKGROUND OF THE INVENTION

It is often desirable to provide a hydrophilic coating (e.g., anti-fogcoating) on a substrate such as an automotive windshield, automotivewindow, automotive mirror, architectural mirror, bathroom mirror, or thelike. Such coatings may reduce the likelihood of water drops depositedon the substrate taking globular shape(s), thereby enabling visibilityto be improved. In other words, hydrophilic coatings function to reducebead-like condensation on substrate surfaces (e.g., on the interiorsurface of an automotive windshield or window). A hydrophilic coatingcan reduce the formation of many tiny droplets of liquid, which canscatter light, on a surface (i.e., make condensation on a surfacefilm-wise as opposed to droplet-wise).

Unfortunately, certain hydrophilic coatings are not as durable and/orhard as would otherwise be desired and thus are not efficient from apractical point of view for applications such as automotive windshieldsand/or other types of windows.

In view of the above, it is apparent that there exists a need in the artfor (i) a coated article (e.g. coated glass or plastic substrate) havinghydrophilic properties, and a method of making the same, and/or (ii) aprotective hydrophilic coating for window and/or mirror substrates thatis somewhat resistant to scratching, damage, or the like.

It is a purpose of different embodiments of this invention to fulfillany or all of the above described needs in the art, and/or other needswhich will become apparent to the skilled artisan once given thefollowing disclosure.

SUMMARY OF THE INVENTION

An object of this invention is to provide a durable coated article thatit is less likely to attract or be affected by bead-like liquidcondensation. Exemplary applications to which such hydrophiliccoating(s) may be applied include, for example without limitation,automotive windshields, automotive backlites (i.e., rear vehiclewindows), automotive side windows, architectural windows, mirrors, etc.

Another object of this invention is to provide a scratch resistanthydrophilic coating for use in conjunction with a coated article.

Another object of this invention is to form or provide a hydrophiliccoating by doping diamond-like carbon (DLC) with at least one polarinducing dopant(s) such as, for example, boron (B) and/or nitrogen (N).In certain embodiments, the atomic percentage of the polar inducingdopant(s) (e.g., B and/or N dopants, but not including H dopants thatmay or may not be added because H is not a polar inducing dopant) is nogreater than about 10%, more preferably no greater than about 5%, andmost preferably no greater than about 4%. A polar inducing dopant is adopant that causes DLC to become more graphitic (e.g., cause more sp²bonds), as opposed to more tetrahedral (i.e., more sp³ bonds). Polarinducing dopant(s) tend to cause the DLC inclusive layer to be morepolar, which in turn increases surface energy and thus provides for amore hydrophilic coating.

Another object of this invention is to provide a coated article, whereina layer of the coating includes both sp² and sp³ carbon-carbon bonds andhas a wettability W with regard to water of at least about 700 mN/m,more preferably at least about 750 mN/m, and most preferably at leastabout 800 mN/m. This can also be explained or measured in Joules perunit area (mJ/m²).

Another object of this invention is to cause contact angle θ of a DLCinclusive layer or coating to decrease due to ultraviolet (UV) exposure.The contact angle before such exposure may or may not be hydrophilic,but after said exposure in certain example embodiments the post-UVcontact angle θ is less than about 20 degrees, more preferably less thanabout 15 degrees, even more preferably less than about 10 degrees, andeven more preferably less than about 8 degrees.

Another object of this invention is to provide a coated article, whereina layer of the coating includes both sp² and sp³ carbon-carbon bonds andhas a surface energy Υ_(c) of at least about 24 mN/m, more preferably atleast about 26 mN/m, and most preferably at least about 28 mN/m.

Another object of this invention is to provide a coated article, whereina DLC inclusive layer of the coating has an initial (i.e. prior to beingexposed to environmental tests, rubbing tests, acid tests, UV tests, orthe like) water contact angle θ of no greater than about 10 degrees,more preferably no greater than about 8 degrees, even more preferably nogreater than about 6 degrees, and most preferably no greater than about4 degrees. The article's initial contact angle θ may be as low as 1–3degrees in certain embodiments. In certain embodiments the article'scontact angle may increase over time upon exposure to environmentalelements (as graphitic sp² C—C bonds wear off) while in otherembodiments the article's contact angle may decrease over time upon suchexposure.

Another object of this invention is to provide a hydrophilic DLCinclusive layer for coating a substrate. In at least one portion of thelayer no more than about 70% of the bonds in that portion of the layerare of the sp³ type, and more preferably no more than about 60% of thebonds are of the sp³ type. A substantial portion of the remainder of thebonds may be of the graphitic or sp² type. The bonds in the layer mayinclude, for example, carbon-carbon (C—C) bonds, carbon-nitrogen (C—N)bonds, carbon-boron (C—B) bonds, and/or carbon-hydrogen (C—H) bonds. Thesp³ type bonds (e.g., C—C bonds) function to increase the hardness andscratch resistance of the coating, while the graphitic sp² type bonds(e.g., C—C, C—N and/or C—B bonds) cause the coating to be morehydrophilic and have a lower contact angle.

Another object of this invention is to provide a coating which can makeaccumulated condensation form in a more film-wise manner; as opposed toa droplet-wise manner.

Still another object of this invention is to form amine (NH₂) functionalgroups near the surface of a hydrophobic coating or layer so as toenhance hydrophilicity.

Yet another object of this invention is to fulfill one or more of theabove listed objects and/or needs.

Certain example embodiments of the instant invention fulfill one or moreof the above-listed objects or needs by providing a coated glass articlecomprising:

a glass substrate;

a layer comprising diamond-like carbon (DLC) with sp³ carbon-carbonbonds provided on said glass substrate; and

wherein said layer comprising DLC is ultraviolet (UV) radiation exposedso as to cause the layer to have a contact angle θ with a drop of waterthereon of no greater than about 20 degrees.

Other example embodiments of the instant invention fulfill one or moreof the above-listed objects or needs by providing a method of making acoated article, the method comprising:

ion beam depositing a diamond-like carbon (DLC) inclusive layer on asubstrate; and

exposing the DLC inclusive layer to ultraviolet (UV) radiation in amanner sufficient to cause a contact angle θ of the DLC inclusive layerto decrease by at least about 20%.

Still further example embodiments of the instant invention fulfill oneor more of the above-listed objects and/or needs by providing a coatedarticle comprising a DLC inclusive layer supported by a glass substrate,wherein the DLC inclusive layer has a contact angle θ less than or equalto 10 degrees.

This invention will now be described with respect to certain embodimentsthereof, along with reference to the accompanying illustrations.

IN THE DRAWINGS

FIG. 1 is a side cross sectional view of a coated article according toan embodiment of this invention, wherein a glass or plastic substrate isprovided with a hydrophilic coating thereon including a DLC inclusivelayer.

FIG. 2 is a side cross sectional view of a coated article according toanother embodiment of this invention, wherein a glass or plasticsubstrate is provided with a hydrophilic coating thereon including a DLCinclusive layer.

FIG. 3 is a side cross sectional view of a coated article according toanother embodiment of this invention, wherein a glass or plasticsubstrate is provided with a hydrophilic coating thereon including a DLCinclusive layer.

FIG. 4 is a side cross sectional partially schematic view illustrating acontact angle θ of a drop (e.g., sessile drop of water) on an uncoatedglass substrate.

FIG. 5 is a side cross sectional partially schematic view illustrating ahigh contact angle θ of a drop on a coated article including ahydrophobic coating of, for example, an article disclosed in relatedapplication Ser. No. 09/442,805.

FIG. 6 is a side cross sectional partially schematic view illustrating alow contact angle θ of a drop (e.g., sessile drop of water) on a coatedarticle according to an embodiment of this invention.

FIG. 7 is a side cross sectional view of a linear ion beam source whichmay be used in any embodiment of this invention for depositing a DLCinclusive hydrophilic layer(s).

FIG. 8 is a perspective view of the linear ion beam source of FIG. 7.

FIG. 9 is a flowchart illustrating steps taken according to anotherembodiment of this invention where a DLC inclusive layer is exposed toultraviolet (UV) light/radiation in order to lower contact angle θthereof.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS OF THIS INVENTION

Referring now more particularly to the accompanying drawings in whichlike reference numerals indicate like elements throughout theaccompanying views.

Certain embodiments of this invention relate to improving hydrophilicqualities of a coated article (e.g., automotive windshield, automotivebacklite, automotive side window, snow-mobile windshield, architecturalwindow, mirror, etc.) by providing a diamond-like carbon (DLC) inclusivelayer or coating on a substrate in a manner such that the resultingarticle and/or layer has hydrophilic qualities or characteristics. Oneway of providing DLC with hydrophilic characteristics has been found tobe by doping DLC with at least one polar inducing dopant (e.g., Nitrogen(N), Boron (B), and/or any other suitable polar inducing dopant), theDLC inclusive layer may be made more polar so as to have a highersurface energy and thus be more hydrophilic.

In other embodiments of this invention, a DLC inclusive layer (e.g.,having a contact angle θ from 5–100 degrees) may be exposed toultraviolet (UV) radiation in order to lower the contact angle θ of theDLC inclusive layer to, for example, a hydrophilic range. Optionally,the DLC inclusive layer may be exposed to water at the same time as theUV exposure in order to speed up the process of contact angle θreduction. The UV exposure embodiment may be used either in combinationwith, or separately from, the aforesaid doping embodiment in order toprovide a hydrophilic coating.

In doping embodiments of this invention, the provision of the at leastone polar inducing dopant increases the polar component of the DLCinclusive layer's surface energy, which in turn increases the layer'stotal surface energy. The higher the surface energy, the morehydrophilic the layer and the lower the contact angle θ. Thus, byincreasing the surface energy via the dopant(s), the hydrophilicity canbe improved and thus the contact angle θ can be lowered.

Combining the hydrophilicity with the use of an amorphous diamond-likecarbon (DLC) layer/coating provided on the base substrate enables theresulting coated article to have a low contact angle θ as well assurface hardness and scratch resistant characteristics sufficient suchthat the article may be used in automotive and other high exposureenvironments where durability is desired.

FIG. 1 is a side cross-sectional view of a coated article according toan embodiment of this invention, wherein at least one diamond-likecarbon (DLC) inclusive protective coating(s) or layer 3 is provided onsubstrate 1. The coated article has an exterior or outer surface 9.Substrate 1 may be of glass, plastic, ceramic, or the like.

In doping embodiments, layer or coating 3 includes at least one polarinducing dopant therein which causes bonds in the DLC inclusive layer tobe more polar, which in turn causes a higher surface energy and lowercontact angle θ. The dopant(s) cause more graphitic or polar sp² typebonds (e.g., C—C sp² type bonds, C—N sp² type bonds, and/or C—B s typebonds) to be formed in layer 3 so that the layer includes both sp² typeand sp³ type (e.g., C—C sp³ type) bonds. When more bonds in layer 3become polar, this results in water being more attracted to the layer 3since water is polar. The tetrahedral amorphous sp³ type C—C bonds(ta-C) provide the layer 3 with acceptable hardness and/or scratchresistance characteristics while the sp² type C—C and C-dopant bondsimprove the layer's hydrophilicity. Preferably, a substantial portion ofthe carbon in layer 3 is in amorphous or disordered form (as opposed tocrystalline form for example).

The dots in layer/coating 3 in FIG. 1 illustrate the dopant, which isshown as being relatively evenly or uniformly distributed throughout thethickness of layer 3. As evident from the above, exemplarypolar-inducing dopants include, but are not limited to, Nitrogen (N),Boron (B), Phosphorous (P), As, S, Sb, Ga, In, and the like. Dopantssuch as N and B may be used either alone or in combination to dope theDLC inclusive layer 3 in certain embodiments so as to improve thelayer's hydrophilicity. Layer 3 functions in a hydrophilic manner (i.e.it is characterized by low contact angles θ and/or high surfaceenergies) so as to reduce the occurrence of bead-like condensationforming on the coated article. Hydrophilic characteristics may beadvantageous in environments such as bathroom mirror surfaces, interiorsurfaces of automotive windshields or windows, and the like.

In UV exposure embodiments (which may be carried out in combination withdoping embodiments, or without doping), DLC inclusive layer 3 may or maynot have the aforesaid dopant(s) therein. More particularly, in UVexposure embodiments, the DLC inclusive layer 3 as deposited may behydrophilic, or may be non-hydrophilic (i.e., layer 3 as deposited mayhave a contact angle θ of any value from 5–100 degrees). Exposure of thelayer 3 to UV radiation (and optionally water) causes the contact angleof the layer 3 to decrease (e.g., to hydrophilic range(s)). Thus,following a significant amount of UV exposure, the contact angle θ ofthe DLC inclusive layer 3 in UV exposure embodiments is preferably lessthan about 20 degrees, more preferably less than about 15 degrees, evenmore preferably less than about 10 degrees, and most preferably lessthan about 8 degrees.

In certain embodiments, hydrophilic layer 3 may be from about 10 to1,000 Angstroms thick, more preferably from about 50 to 200 Angstromsthick. In one exemplary embodiment, layer 3 may be about 100 Angstromsthick. Moreover, in certain exemplary embodiments of this invention,layer 3 has an average hardness of at least about 10 GPa, morepreferably of at least about 20 GPa, even more preferably of at leastabout 50 GPa, and most preferably from about 50–600 GPa. In certainembodiments, layer 3 may have an average hardness of about 75 GPa. Layer3 preferably has good abrasion resistance, a coefficient of friction offrom about 0.05 to 0.20 (e.g., 0.15), and an average surface roughnessof no greater than about 0.3 nm. Because of the presence of both the sp²type and sp³ type bonds in layer 3, the layer preferably has a densityof at least about 2.4 grams/cm² (more preferably from about 2.5 to 3.0grams/cm²). Layer 3 is preferably corrosion resistant, even in thecontext of significant humidity and/or heat. Layer 3 may also be inertto acids, alkalis, solvents, salts, and/or water in certain embodimentsof this invention. Thus, layer 3 may act as a barrier to chemicalattacks on the underlying substrate 1 (e.g., a soda-lime-silica glasssubstrate).

Hydrophilic layer 3 has one surface exposed to the air or theatmosphere. In doping embodiments, layer 3 after it has been doped tomake it more hydrophilic, has a much lower contact angle θ with asessile drop of water than it otherwise would without doping. In certaindoping embodiments of this invention, layer 3 has an initial contactangle θ with a sessile drop of water of no greater than about 10degrees, more preferably of no greater than about 8 degrees, even morepreferably of no greater than about 6 degrees, and most preferably nogreater than about 4 degrees. In certain embodiments, the contact anglemay be as low as 1–3 degrees. As mentioned above, in certain UV exposureembodiments, the contact angle of layer 3 may be brought down from anon-hydrophilic range into a hydrophilic range upon exposure of thelayer to significant UV rays.

In certain doping embodiments of this invention, the amount of polarinducing dopant material (one or more dopants) in hydrophilic layer 3 isfrom about 1–30%, atomic percentage, more preferably from about 1–10%,even more preferably from about 1–5%, and most preferably from about1–4%. In certain embodiments, polar inducing dopant(s) in layer 3 mayrepresent about 3–4% (atomic) of the atoms in layer 3. The remainder maybe C and/or H in certain embodiments. In certain instances, it has beenfound that increasing the dopant percentage by too much can decrease thediamond like properties of the layer 3, making the layer too graphiticfor practical applications in certain circumstances (e.g., the moregraphitic the coating the darker and less transmissive/transparent itbecomes). Since the DLC inclusive layer 3 is only doped with low amountsof polar inducing dopant(s) such as B and/or N, much of the diamond-likenature of the bonding in layer 3 is preserved. Other types of dopant(e.g., H is not a polar inducing dopant) may or may not be provided inlayer 3 in certain embodiments.

Thirteen exemplary make-ups of a doped hydrophilic layer 3 are set forthbelow in Chart No. 1, these exemplary make-ups being applicable to anydoping embodiment herein including any of the embodiments of FIGS. 1–3.

CHART NO. 1 Polar Atomic % C Atomic % N Atomic % B Component Atomic % H97 1.5 1.5  6 0 97 2.1 0.9 10 0 96 3.0 1.0  7 0 87 2.1 0.9 — 10.0 89 2.01.0 — 8.0 96 4.0 0.0 — 0 97 0 3.0 — 0 70 10.0 0 — 20.0 75 0 5.0 — 20.071 7 0 — 22.0 69 6 0 — 25.0 68 0 8 — 24.0 67 9 0 — 25.0

Layers or films 3 doped independently with either N or B have been foundto be hydrophilic. However, it has also been found that additionalsurprising hydrophilic properties may result when a mixture of dopants(e.g., N and B) is used to dope DLC inclusive layer 3. In certainembodiments, the ratio of N to B may be approximately 2:1 (N:B). Otherdopants may of course be used; and in UV exposure embodiments dopantsare optional.

Optical characteristics of layer 3, such as n & k refractive indices,and Tauc optical bandgap, can be tailored/adjusted by changing theconcentration or percentage of dopants (e.g., N and/or B) in thelayer/film. The optical bandgap may be varied between 1.75 and 3.2 eV incertain embodiments. The “n” refractive index at 550 nm may be variedbetween, for example, 1.6 and 2.3, while the “k” refractive index at 550nm may be varied between, for example, 0.01 and 0.1 in certainembodiments (permittivity at GHz 4.7). In certain embodiments, a highbandgap (e.g., above 3 eV) and/or an absorption coefficient greater thanabout 10⁶ cm⁻¹ implies that such films/layers 3 are ultraviolet (UV)absorbing. Strong binding energy also implies strong UV radiationresistance. In certain embodiments, UV transmission of layer 3 at 350 nmis no greater than about 40% (preferably no greater than about 35%).

In FIG. 1 doping embodiments, the dopant(s) may be distributed in afairly uniform manner throughout the thickness of layer 3, asillustrated. For example, dopant inclusive gas may be provided in an iondeposition apparatus throughout the entire course of the depositionprocess for layer 3.

In the FIG. 2 embodiment, the dopant(s) is/are not uniformly distributedthroughout the entire thickness of hydrophilic layer 3. Instead, a moresignificant portion of dopant(s) is provided near the exterior surfaceof layer 3 than near the interface between layer 3 and substrate 1, asshown in FIG. 2. The presence of the dopant(s) at or near the exteriorsurface of layer 3 enables the bonds near the layer's surface to be moregraphitic. Thus, layer 3 still has the hydrophilic properties describedherein (e.g., low contact angle(s). For example, in certain embodimentsthe outermost 10 angstrom (A) thick portion (or 10 nm thick portion inother embodiments) of layer 3 may include at least about 3% dopant atoms(e.g., N, B, P, As, Sb, Ga, and/or In), more preferably at least about5%, and most preferably at least about 7%. The provision of these polarinducing dopant atoms near the coating's surface results in a more polarcoating surface. The rest of layer 3 (i.e., the middle of layer 3 and/orthe portion of layer 3 adjacent the substrate or some intermediatelayer) may be of or include undoped DLC in certain embodiments, oralternatively may be of or include DLC doped with Si, O, or H. Thisenables many of the graphitic sp² type bonds to be located at or nearthe exterior surface of layer 3. Too many sp² type bonds in layer 3 canundesirably reduce its transparency or transmission characteristics, soin some embodiments it may be desirable to minimize the presence of sp²type bonds at locations other than at or near the exterior surface wherethey are needed to lower the contact angle θ of the layer 3.

In an exemplary embodiment of this invention (see the tenth listedexemplary make-up listed above in Chart No. 1), where the C is dopedwith N and H, it has been found that the provision of the N causes amine(NH₂) functional groups to be formed at or near the surface of layer 3.In such amine groups, for example, one of the N bonds is with a C (sp²)while the other two N bonds are with H. These amine groups enhance thehydrophilic nature of the layer 3 and thus of the coated article. Inexemplary amine inclusive embodiments, the layer may include from about60–84% C, from about 1–12% B, and from about 4–39% H (atomic); and morepreferably from about 65–75% C, from about 5–10% B, and from about15–30% H.

FIG. 3 illustrates that in certain embodiments of this invention, atleast one intermediate layer 2 may be provided between substrate 1 andthe one or more hydrophilic layer(s) 3. Thus, both layer(s) 3 andlayer(s) 2 are deposited on, and provided on, substrate 1 in thisembodiment. Any desired layer may be utilized as an intermediate layer2. For example, intermediate layer 2 may include a low-E layeringsystem, another DLC inclusive layer, a silicon oxide layer, a siliconnitride layer, and/or a titanium oxide layer in certain embodiments ofthis invention. The term “on” (with regard to a layer being “on” asubstrate or other layer) herein means supported by, regardless ofwhether or not other layer(s) are provided therebetween. Thus, forexample, DLC inclusive layer 3 may be provided directly on substrate 1as shown in FIGS. 1–2, or may be provided on substrate 1 with a low-E orother layer(s) therebetween as shown in FIG. 3. Exemplary layer systems(in full or any portion of these coatings) that may be used as low-E orother coating(s) 2 on substrate 1 between layer 3 and the substrate areshown and/or described in any of U.S. Pat. Nos. 5,837,108, 5,800,933,5,770,321, 5,557,462, 5,514,476, 5,425,861, 5,344,718, 5,376,455,5,298,048, 5,242,560, 5,229,194, 5,188,887 and 4,960,645, which are allhereby incorporated herein by reference.

In certain embodiments, in at least one portion of DLC inclusive layer 3no more than about 70% of the bonds in the layer are of the sp³ type,and more preferably no more than about 60% of the bonds in the layer areof the sp³ type, so that this portion of the layer may attainhydrophilic characteristics. In certain preferred embodiments, no morethan about 50% of the bonds in layer 3 are of the sp³ type (e.g., sp³type C—C bonds), or in other embodiments this may be the case only nearthe exterior or outer surface of layer 3. A substantial portion of theremainder of the bonds are of the graphitic or sp² type. The bonds inthe layer may include, for example, carbon-carbon (C—C) bonds,carbon-nitrogen (C—N) bonds, carbon-boron (C—B) bonds, and/orcarbon-hydrogen (C—H) bonds. The sp³ type bonds (e.g., C—C bonds)function to increase the hardness and scratch resistance of the coating,while the graphitic sp² type bonds (e.g., C—C, C—N and/or C—B bonds)cause the coating to be more hydrophilic and have a lower contact angle.It has been found that different techniques may be used to increase thenumber of graphitic sp² type bonds, including but not limited to a)doping as discussed herein, b) heating up the underlying substrateduring the layer 3 deposition process, and/or c) utilizing a higher ionenergy eV energy during the layer 3 deposition process (e.g., from about200–600 eV, most preferably from about 375 to 425 eV). Also, the aminefunctional groups discussed above may also function to enhance thehydrophilic nature of the article. A higher eV energy used during theion deposition process of layer 3 results in less sp³ type bonds andmore sp² type bonds. Techniques b) and/or c) may be used in combinationwith the doping herein to obtain hydrophilic characteristics.

In certain embodiments, DLC inclusive layer 3 and/or the coating systemon substrate 1 is/are at least about 75% transparent to or transmissiveof visible light rays, preferably at least about 85%, and mostpreferably at least about 95%.

When substrate 1 is of glass, the glass may be from about 1.5 to 5.0 mmthick, preferably from about 2.3 to 4.8 mm thick, and most preferablyfrom about 3.7 to 4.8 mm thick. Conventional soda lime silica glass maybe used as substrate 1 in certain embodiments, such glass beingcommercially available from Guardian Industries, Corp., Auburn Hills,Mich. In certain other embodiments of this invention, substrate 1 may beof borosilicate glass, or of substantially transparent plastic. In stillfurther embodiments, an automotive window (e.g. windshield, backlite, orside window) including any of the above glass substrates laminated to aplastic substrate may combine to make up substrate 1, with a coatingsystem of any of FIGS. 1–3 provided on a surface of such a substrate toform the window. In other embodiments, substrate 1 may include first andsecond glass sheets of any of the above mentioned glass materialslaminated to one another, for use in window (e.g. automotive windshield,residential window, commercial architectural window, automotive sidewindow, vacuum IG window, automotive backlite or back window, etc.)and/or other environments.

When substrate 1 of any of the aforesaid materials is coated with atleast DLC inclusive layer 3 according to any of the FIGS. 1–3embodiments, the resulting coated article has the followingcharacteristics in certain example non-limiting embodiments: visibletransmittance (Ill. A) greater than about 60% (preferably greater thanabout 70%, and most preferably greater than about 80%), UV (ultraviolet)transmittance less than about 38%, total solar transmittance less thanabout 45%, and IR (infrared) transmittance less than about 35%(preferably less than about 25%, and most preferably less than about21%). Visible, “total solar”, UV, and IR transmittance measuringtechniques are set forth in U.S. Pat. No. 5,800,933.

Hydrophilic performance of coating/layer 3 in any of the aboveembodiments is a function of contact angle θ, surface energy Υ, and/orwettability or adhesion energy W. The surface energy Υ of layer 3 may becalculated by measuring its contact angle θ. Exemplary contact angles θare illustrated in FIGS. 4–6. A hydrophilic coating or layer system 3according to an embodiment of this invention is on the substrate of FIG.6, while no coating of any kind is on the substrate of FIG. 4 and ahydrophobic coating is on the substrate of FIG. 5. No coatings areillustrated in FIGS. 4 and 6 for purposes of simplicity. To measurecontact angle in one embodiment, a sessile drop 31 of a liquid such aswater is placed on the substrate as shown in FIGS. 4–6. A contact angleθ between the drop 31 and underlying article appears, defining an angleθ depending upon the interface tension between the three phases at thepoint of contact. The contact angle is greater in FIG. 5 than in FIG. 4,because the coating layer on the substrate in FIG. 5 is hydrophobic(i.e., results in a higher contact angle). However, due to thisinvention, the contact angle θ in FIG. 6 is much lower than in either ofFIGS. 4–5.

Generally, the surface energy Υ_(c) of a layer 3 or any otherarticle/layer can be determined by the addition of a polar and adispersive component, as follows: Υ_(c)=Υ_(CP)+Υ_(CD), where Υ_(CP) isthe layer's/coating's polar component and Υ_(CD) the layer's/coating'sdispersive component. The polar component of the surface energyrepresents the interactions of the surface mainly based on dipoles,while the dispersive component represents, for example, van der Waalsforces, based upon electronic interactions. Generally speaking, thehigher the surface energy Υ_(c) of layer 3, the more hydrophilic thelayer (and coated article) and the lower the contact angle θ.

Adhesion energy (or wettability) W can be understood as an interactionbetween polar with polar, and dispersive with dispersive forces, betweenthe exterior surface 9 of the coated article and a liquid thereon suchas water. Υ^(P) is the product of the polar aspects of liquid tensionand article tension; while Υ^(D) is the product of the dispersive forcesof liquid tension and article tension. In other words,Υ^(P)=Υ_(LP)*Υ_(CP); and Υ^(D)=Υ_(LD)*Υ_(CD); where Υ_(LP) is the polaraspect of the liquid (e.g. water), Υ_(CP) is the polar aspect ofcoating/layer 3; Υ_(LD) is the dispersive aspect of liquid (e.g. water),and Υ_(CD) is the dispersive aspect of coating/layer 3. It is noted thatadhesion energy (or effective interactive energy) W, using the extendedFowkes equation, may be determined by:W=[Υ_(LP)*Υ_(CP)]^(1/2)+[Υ_(LD)*Υ_(CD)]^(1/2)=Υ_(l)(1+cos θ),where Υ_(l) is liquid tension and θ is the contact angle. W of twomaterials (e.g. layer 3 and water thereon) is a measure of wettabilityindicative of how hydrophilic the layer or coated article is.

When analyzing the degree of hydrophilicity of layer 3 or a coatedarticle herein with regard to water, it is noted that for water Υ_(LP)is 51 mN/m and Υ_(LD) is 22 mN/m. In certain embodiments of thisinvention, the polar aspect Υ_(CP) of surface energy of layer 3 is atleast about 5, and more preferably at least about 7, and most preferablyfrom about 7–10 (variable or tunable between 5 and 15 in certainembodiments) and the dispersive aspect Υ_(CD) of the surface energy oflayer 3 is from about 16–22 mN/m (more preferably from about 18–20mN/m).

Using the above-listed numbers, according to certain embodiments of thisinvention, the surface energy Υ_(C) of layer 3 is at least about 24mN/m, more preferably at least about 26 mN/m, and most preferably atleast about 28 mN/m; and the adhesion energy W between water and layer 3is at least about 600 mN/m, more preferably from about 700–1,300 mN/m,even more preferably from about 750–950 mN/m, and most preferably fromabout 800–950 mN/m. These high values of adhesion energy W and layer 3surface energy Υ_(C), and the low initial contact angles θ achievable,illustrate the improved hydrophilic nature of coated articles accordingto different embodiments of this invention.

The initial contact angle θ of a conventional glass substrate 1 withsessile water drop 31 thereon is typically from about 22–24 degrees, asillustrated in FIG. 4 (although it may be as low as 18 degrees incertain instances). Thus, conventional glass substrates are not ashydrophilic as embodiments of this invention. Moreover, layers 3 hereinprovide for scratch resistance and/or high durability. A normal ta-Clayer, undoped, on a glass substrate is not as hydrophilic asembodiments of this invention. Inventions herein enable the contactangle of a ta-C inclusive layer 3 to be reduced to improve thehydrophilicity of a coated article, as shown by the low contact angle θin FIG. 6.

Another advantage associated with certain layers 3 according to certainembodiments of this invention is that the layer 3 may becomeelectrically conductive so as to reduce the likelihood of a build-up ofstatic electricity. This reduction in resistivity is believed to be dueto the doping described herein. For example, prior to doping resistivityof a ta-C layer may be, e.g., 10⁸ ohms/cm, whereas after doping theresistivity may drop to, e.g., less than about 500 ohms/cm, morepreferably less than about 100 ohms/cm, most preferably from about 0.01to 50 ohms/cm.

Layer 3 may have a dielectric constant of from about 8 to 12 at 10 kHz,preferably about 10, and may have a dielectric constant of about 2 to 6at 100 MHz, preferably about 4. In certain embodiments, layer 3 may havean electrical breakdown strength (V cm⁻¹) of about 10⁶. As for thermalproperties, layer 3 may have a thermal coefficient of expansion of about9×10⁻⁶/C, and a thermal conductivity of about 0.1 Wcm K.

FIGS. 7–8 illustrate an exemplary linear or direct ion beam source 25which may be used to deposit layer(s) 3, clean a substrate 1, or surfaceplasma treat a DLC inclusive layer to add doping atoms thereto accordingto different embodiments of this invention. Ion beam source 25 includesgas/power inlet 26, racetrack-shaped anode 27, grounded cathode magnetportion 28, magnet poles 29, and insulators 30. A 3 kV DC power supplymay be used for source 25 in some embodiments. Linear source iondeposition allows for substantially uniform deposition of DLC inclusivelayer 3 as to thickness and stoichiometry.

Ion beam source 25 is based upon a known gridless ion source design. Thelinear source is composed of a linear shell (which is the cathode andgrounded) inside of which lies a concentric anode (which is at apositive potential). This geometry of cathode-anode and magnetic field33 gives rise to a close drift condition. The magnetic fieldconfiguration further gives rise to an anode layer that allows thelinear ion beam source to work absent any electron emitter. The anodelayer ion source can also work in a reactive mode (e.g., with oxygenand/or nitrogen). The source includes a metal housing with a slit in ashape of a race track as shown in FIGS. 7–8. The hollow housing is atground potential. The anode electrode is situated within the cathodebody (though electrically insulated) and is positioned just below theslit. The anode can be connected to a positive potential as high as3,000 volts. Both electrodes may be water cooled in certain embodiments.

Feedstock gases are fed through the cavity 41 between the anode andcathode. The linear ion source also contains a labyrinth system thatdistributes the precursor gas evenly along its length and which allowsit to supersonically expand between the anode-cathode space internally.The electrical energy then cracks the gas to produce a plasma within thesource. The ions are expelled out and directed toward the substrate 1 onwhich the layer(s) 3 is to be grown. The ion beam emanating from theslit is approximately uniform in the longitudinal direction and has agaussian profile in the transverse direction. Exemplary ions 34 areshown in FIG. 7. A linear source as long as 0.5 to 3 meters may be madeand used, although sources of different lengths are anticipated indifferent embodiments of this invention. Electron layer 35 is shown inFIG. 7 and completes the circuit thereby enabling the ion beam source tofunction properly.

Exemplary methods of depositing a DLC inclusive hydrophilic layer 3 overtop of and on a substrate 1 (the substrate may have other layer(s)(e.g., layer 2) already provided thereon) will now be described. Thesemethods are for purposes of example only and are not intended to belimiting. The energies used during the deposition process of layer 3and/or the directionality provided by the ion beam deposition techniquesenable layer 3 to be fairly uniformly deposited over all aspects of theunderlying structure.

Prior to layer 3 being formed on substrate 1, the top surface ofsubstrate 1 may be cleaned by way of a first linear or direct ion beamsource. For example, a glow discharge in argon (Ar) gas or mixtures ofAr/O₂ (alternatively CF₄ plasma) may be used by the source to remove anyimpurities on the substrate surface. Preferably, no oxygen orfluorocarbons are used since in the next step doping with N and/or Batoms takes place. Such interactions are physio-chemical in nature. Thepower density may be, for example, 1 Watt/cm². Substrate 1 may also becleaned by, for example, sputter cleaning the substrate prior to actualdeposition of layer 3. While cleaning may be performed in someembodiments, it need not be performed in other embodiments of thisinvention.

Then, the deposition process for DLC inclusive layer 3 on substrate 1may be performed using the linear ion beam source and correspondingdeposition technique as illustrated in FIGS. 7–8 (e.g., see linear ionbeam 25). The ion beam source 25 (which may be the same or a differentsource than the cleaning ion beam source) functions to deposit a ta-Cinclusive layer 3 (hydrogenated in certain embodiments) on substrate 1,along with dopants (e.g., N and/or B) therein. Exemplary feedstock gaseswhich may be used include Nitrogen gas, diborane gas, and/or C₂H₂ gas.

Alternatively, layer 3 may be deposited using a filtered cathodic vacuumarc ion beam apparatus (FCVA-IB) as disclosed in “Tetrahedral AmorphousCarbon Deposition, Characterisation and Electronic Properties”, byVeerasamy, Cambridge 1994 (incorporated herein by reference). Thisdeposition process may be achieved just after a plasma clean of thesubstrate 1 using the same deposition chamber, or another chamber. Insuch techniques, a cathodic arc discharge of an ultrapure carbon targetmay be triggered in a base vacuum of, e.g., <10⁻⁶ Torr. A targetconsisting essentially of Hoescht carbon may be machined into acylindrical electrode about 90 mm in diameter and about 50 mm deep.Conditions of arc discharge may be, e.g., 70 A and 17 V. The pressureduring the cathodic arc process may be in the range of a tenth of amTorr. One, two, or more dopant gas(es) may be simultaneously introducedinto the toroidal bend region. Exemplary gases may be diborane(including a dopant B) and Nitrogen. Gas flows may be controlled by twomass flow controllers in series with a needle valve. The diborane gasmay be independently flowed through such a controller. The power iscoupled by plasma collisions to the dopant gas diborane and Nitrogenmixture which may be introduced via a mass flow controller at the bendof the magnetic filter. An exemplary torroidal magnetic field may be 100mTesla. The energetic carbon ions and high energy electrons togetherwith the UV radiation produced by the arc dissociate(s) the gas mixtureinto extremely reactive energetic ions. In general, only ionized species(e.g., C, N, and B) are constrained to follow the toroidal magneticfield in the filter while the neutrals and macroparticles are filteredout. The flux of ionized atoms is/are transported to the growth surfaceon the substrate 1 so that layer 3 is formed. The ion energy can beindependently varied by a grid which has a negative potential or RF biason the substrate to tune the physical properties of the layer 3. Therange of self bias potential is from, for example, −1,000 to +1,000 V.In certain embodiments, a window of 120–200 V per ion species may beused. Partial pressures used during the deposition may be, for example,from 10⁻⁶ to 10⁻⁴ Torr. Exemplary parameters which may be used in such adeposition process are: base pressure of 10⁻⁶, N₂ gas 0–5 sccm, B₂H₄ gas0–2 sccm, a room temperature for substrate 1, and an arc power of 1,000W. In such a manner, layer 3 including amorphous DLC doped with B and/orN may be formed on substrate 1.

The hydrophilic nature of layer 3 may be enhanced in certain embodimentsby using a plasma treatment or grafting procedure which adds certainpolar functional groups at the surface of layer 3, altering the chemicalreactivity at the surface while the bulk properties of the layer remainsubstantially unaffected. In such embodiments, a plasma of Nitrogen gas(N₂) may be used at a pressure of about 1 mT to enhance the hydrophilicnature.

In one instance, ta-C films having thicknesses from 10 to 50 nm weredeposited on quartz substrates with an interdigitated planar array of 20μm Ni electrodes. These electrodes were prepared by conventionallithographic techniques. The influence of the adsorbed molecules on theelectrical properties of the ta-C doped films were then studied usingI-C-V characteristics. Strong sensitivity of the I-C-V characteristicswere found in the presence of water and alcohol. The high sensitivity ofthe capacitance on water vapor concentration as well as the quickresponse to water molecules suggested a high polar component of thesurface bonds. A layer 3 of ta-C:N:B also has a high density asevidenced by its high plasmon peak at about 32.9 eV.

When it is desired to hydrogenate layer 3, for example, a dopant gas maybe produced by bubbling a carrier gas (e.g. C₂H₂) through the precursormonomer (e.g. TMS or 3MS) held at about 70 degrees C (well below theflashing point). Acetylene feedstock gas (C₂H₂) is used in certainembodiments to prevent or minimize/reduce polymerization and to obtainan appropriate energy to allow the carbon and/or hydrogen ions topenetrate the article and subimplant therein, thereby causing the layer3 to grow. Other suitable gases, including polar inducing dopant gases,may also be used in the source to create the ions 34.

As mentioned above, in addition to doping, it has been found that thelayer 3 may be made more hydrophilic in nature as a function of how itis deposited on substrate 1. The temperature of substrate 1 may beraised during the deposition process (e.g., to about 100–300 degreesC.). An alternative way in which to make the layer more hydrophilic isto increase the ion energy used during the deposition process, e.g., toabout 200 to 500 eV, most preferably about 400 eV, in order to reducesp³ bonding content in the layer 3. In other embodiments of thisinvention (doping and/or UV exposure embodiments), a base portion oflayer 3 may be ion beam deposited at a rather high ion energy (e.g.,750–1500 eV per two C atoms) and then for deposition of the top portionof the layer 3 the ion energy is lowered to a lower level (e.g., from10–200 eV per two C atoms) to provide more sp² C—C bonds at the surfaceof layer 3.

While ion beam deposition techniques are preferred in certainembodiments, other methods of deposition may also be used in differentembodiments. For example, filtered cathodic vacuum arc ion beamtechniques may be used to deposit layer 3 as discussed above. Moreover,sputtering techniques may also be used to deposit layer 3 on substrate 1in other embodiments.

FIG. 9 is a flowchart illustrating steps taken according to ultraviolet(UV) exposure embodiments of the instant invention (which may or may notbe doped in different embodiments of this invention). Initially, a DLCinclusive layer 3 is ion beam deposited on a substrate 1 in step S1. TheDLC inclusive layer 3 may or may not be doped as described above. Otherthan the potential for not being doped, DLC inclusive layer 3 is asdescribed in any of the aforesaid embodiments of the instant invention.Layer 3 as originally deposited may or may not be hydrophilic; e.g., thelayer 3 may have a contact angle θ anywhere in the range of from 5–100degrees. The DLC inclusive layer 3 may be deposited directly onsubstrate 1 (see FIG. 1), or alternatively on the substrate 1 overanother layer(s) as described above (see FIG. 3). Following depositionof DLC inclusive layer 3, the layer 3 is exposed to UV radiation/rays instep S2. This exposure to UV radiation may be carried out during theprocess of manufacture (e.g., a UV source for emitting UV rays towardlayer 3 may be located on an apparatus following the ion beam sourceused for depositing layer 3), and/or alternatively the UV exposure maytake place in ambient atmosphere (e.g., letting the coated article withlayer 3 thereon sit outside in the sun/rain). In either case, the DLCinclusive layer 3 is exposed to UV radiation which causes the contactangle θ of the layer 3 to decrease. Optionally, water may be applied tothe layer 3 during the UV exposure to speed up the contact anglereducing process. The resulting decrease in contact angle θ isillustrated in step S3.

It is noted that UV A seems to work well is exposing the layer 3 tocause decrease in contact angle. The “A” type (lower energy) of UV iswavelengths in the range of from 315–380 nm (near UV). Following and/orduring UV exposure, the film remain scratch resistant and hard (e.g.,even after 600 hrs. QUV), and film thickness does not substantiallychange (i.e., does not change by more than 0–5%).

It is believed that UV exposure of the DLC inclusive layer 3 results inoxidation and causes a thin carbon-oxide layer/portion to form at thesurface of the layer 3 (e.g., including —C═O and/or O—C═O bonds). Thisthin at least partially oxidized surface layer portion has a fair amountof attraction to water molecules (polar bonds), thus explaining itshydrophilicity. This thin carbon oxide inclusive layer/portion may befrom about 1–30 Å thick, more likely/preferably about 5–15 Å thick (inthis regard, the high frequency of dots in layer 3 in FIG. 2 can be usedto represent this thin carbon oxide portion at the top surface ofoverall layer 3; in a sense the UV is causing the DLC layer 3 surface tobecome doped with oxygen). This thin carbon oxide portion is believed toseal off the remainder of the layer 3 from the ambient atmosphere, so asto prevent further oxidation (i.e., the bulk of the hard sp³carbon-carbon bonds in the bulk of the layer 3 are thus resistant tooxidation so that the layer maintains its scratch resistance and thelike). This sealing off prevents degradation of the bulk of layer 3,while at the same time providing hydrophilic properties (i.e., lowcontact angle). The layer upon UV exposure also has less propensity fordust to be attracted thereto.

UV EXPOSURE EXAMPLE

The following Example was performed for purposes of illustrating onenon-limiting implementation of a UV exposure embodiment of thisinvention pursuant to FIG. 9. On a 2 mm thick clear glass substrate, aDLC layer 3 was ion beam deposited to a thickness of 14.69 angstroms (Å)using acetylene (C₂H₂) feedstock gas (145 sccm) at a linear velocity of100 inches/minute, at 2970 V and 0.57 amps. The layer 3 was not dopedwith any of the dopants B, N, etc. above. The results was a DLC layer 3of a-taC:H, having an initial contact angle θ of 73.47 degrees. Then,the coated article was QUV exposed for 86 hours (combination of UVradiation and water). The QUV machine was set for cycles of two (2)hours heat (about 60 degrees C.) and humidity (i.e., water) followed bytwo (2) hours of UV light exposure (the UV light/radiation was fromUVA-340 fluorescent bulbs that match the UV spectrum of sunlight aswell). Following the QUV exposure, the coated article includingsubstrate 1 with DLC layer 3 thereon had a contact angle θ which haddropped all the way down to 19.12 degrees; Thus, it can be seen that thecontact angle decreased by about 74% (i.e., 73.47−19.12=54.35; and54.35/73.47=0.7398 or about 74%). Further UV exposure would allow thecontact angle to drop even further. Thus, the DLC layer 3 as depositedwas not hydrophilic, but after significant UV exposure the contact angleθ of the article had dropped down into the hydrophilic range (i.e., lessthan 20 degrees). It can be seen that the UV exposure caused the contactangle of the layer 3 to significantly drop into the hydrophilic range of<=20 degrees.

In certain example embodiments of this invention, the DLC inclusivelayer 3 is exposed to UV radiation (and optionally water/humidity) in amanner (e.g., amount of UV exposure) sufficient to cause the contactangle θ of the layer 3 to decrease by at least about 20%, morepreferably by at least about 30%, even more preferably by at least about50%, and in certain cases (see Example above) by at least about 70%.

It is noted that The term “QUV” herein means that the coated article isexposed to UV radiation and water, using a QUV Accelerated WeatheringTester available from “The Q-Panel Company, Cleveland, Ohio” to simulatesunlight/rain/humidity. This QUV machine exposes the coated article toUV radiation/light using fluorescent UV lamps, and simulates rain anddew with condensing humidity. Coated articles are tested using QUV byexposing them to alternating cycles of light and moisture at controlled,elevated temperatures (typically from 50–90 degrees C.). During thecondensation cycle, a water reservoir in the bottom of the test chamberis heated to produce vapor; and the hot vapor keeps the chamber at about100% relative humidity.

Advantages of certain embodiments of this invention include, forexample, any advantage listed above, the hydrophilic nature of thearticle/layer, the ability of the layer 3 to withstand high temperatureswithout burning, the reduction of resistance so as to reduce thelikelihood of static buildup, the fact that the deposition process maybe performed at low temperature(s) such as room temperature in certainembodiments, the high deposition rates which may be used (e.g., >2nm/s), the fact that the deposition process is scalable to large areadeposition (e.g., >1 square meter), the high throwing power of thedeposition apparatus in its capability of coating to within 5–8% oncurved surfaces of a substrate 1, the smooth nature of layer 3 absentmany if any pinholes, the ability to realize conformal growth of layer3, the ability to use layer 3 in combination with other underlyinglayers such as low-E layers or silicon nitride layers or silicon oxidelayers, and/or the ability to tune the layer's properties by varying theion energy and/or gases used during the deposition process.

Once given the above disclosure, many other features, modifications, andimprovements will become apparent to the skilled artisan. Such otherfeatures, modifications, and improvements are, therefore, considered tobe a part of this invention, the scope of which is to be determined bythe following claims.

1. A method of making a coated article, the method comprising: forming alayer comprising diamond-like carbon (DLC) on a substrate; and exposingthe layer comprising DLC to ultraviolet (UV) radiation so that the layercomprising DLC has a contact angle θ of less than or equal to 20degrees.
 2. The method of claim 1, wherein the layer comprising DLC isformed using an ion beam.
 3. The method of claim 1, wherein the layercomprising DLC has a contact angle of less than or equal to 15 degrees.4. The method of claim 1, wherein the layer comprising DLC has a contactangle of less than or equal to 10 degrees.
 5. The method of claim 1,wherein the layer comprising DLC is ion beam deposited in a manner so asto include hydrogen.
 6. The method of claim 1, wherein the layercomprising DLC has an average hardness of at least 10 GPa.
 7. The methodof claim 1, wherein the layer comprising DLC has an average hardness ofat least 20 GPa.
 8. The method of claim 1, wherein the layer comprisingDLC is provided on the substrate, so that a low-E coating is locatedbetween the substrate and the layer comprising DLC.
 9. The method ofclaim 8, wherein the low-E coating comprises at least one layercomprising silver.
 10. The method of claim 1, wherein the coated articleis a window having a visible transmittance of at least 60%.
 11. Themethod of claim 1, wherein the layer comprising DLC includes sp³carbon-carbon bonds.